Refused permission to protest in Parliament Square, police are staging a "mass queue" to highlight their grievance about pay. How can they do this without breaking the law?

If anyone knows how to operate within the law, it's a police officer.

So those who gathered outside the Palace of Westminster knew not to shout or wave placards.

Nor is what they are doing a protest in the usual sense - it's a queue to lobby their MPs, all wearing white baseball caps emblazoned with the slogan saying "Fair p(l)ay for police".

THE ANSWER

It's not a protest but a "mass queue"

Protesters cannot hold placards, banners or use loudhailers

Police used same tactic in 2002, copied by other groups since the law banned unauthorised protests

Organisers had wanted to hold a march but were refused permission by their colleagues at the Metropolitan Police because Parliament was sitting. Under the Serious Organised Crime and Police Bill, passed in 2005, the Met has to grant approval for protests to be held within a half-mile of the Houses of Parliament.

A Police Federation spokeswoman hoped there would be as many as 10,000 queuing for the "bobby lobby", although as it turned out there were barely hundreds.

"We're policemen and we have to work within the law and we're happy to do that. We're just doing what we did six years ago in 2002 and it worked well then."

Back then they did it because it was a dignified way of getting their point across. This time, with their march on Parliament outlawed, it had greater meaning.

The march was re-routed to avoid Westminster, and in the afternoon, members unable to squeeze into the rally in Central Hall instead formed a line outside the St Stephen's entrance to Parliament to lobby their MPs.

The point, protesters have told the BBC, is to make a highly visible statement.

Thin blue line

So do scores of officers wearing baseball caps and T-shirts making a point constitute a "protest"?

Is this a protest?

The authorities cannot say. A Home Office spokeswoman says it's up to the Met Police to interpret the law. The Met says it's definitely the Home Office's responsibility.

What is certain is that it's a tactic that others have tried before, such as the Stop the War coalition last October.

"We did have banners and it wasn't really a queue, it turned more into a demonstration but we had discussed just marching to Whitehall and then having a queue but the police would not agree to it," says Chris Nineham.

"This is a loophole and I'm pleased the police have become another group that is making its point through one means or another."

Jeremy Corbyn MP, who strongly opposes protests being banned, says: "It's [lobby queuing] a partly-effective tactic but the real issue is that we shouldn't have to accommodate this particular law. We should be allowed to participate in democracy inside and outside Parliament."

Brian Haw has overcome the ban on unauthorised protests, exempted by the High Court after successfully arguing that his one-man protest, which has been going on for seven years, pre-dates the legislation.

But others have been prosecuted, including Mark Barrett, who organised tea parties in Parliament Square in protest at the law change and was fined £250.